Method for forming thread connected dual wall inflatable fabric into compound curvatures



y 6, 1969 R. R. FISHER ET AL 3,442,996

METHOD FOR FORMING THREAD CONNECTED DUAL WALL INFLATABLE FABRIC INTO COMPOUND CURVATURES Filed July 15. 1966 17A Q L w (8 CLAMP AND SEAL PER/PHERY 2a PRESSUR/ZE r0 SLIGHTLY ABOVE AMBIENT PRESSUREV i so HEAT ABOVE THE DEFORMAT/O/V TEMPERATURE OF THE INFLATABLE SYNTHETIC FABRIC LPOSlT/l/ELY FORM TO DES/RED SHAPE [COOL 7'0 BELOW DEFORMAT/ON TEMPERATUREI i 6 LRELEASE THE POSITIVE FORM/N6 ADD FLEX/BLE SKI/V T0 BOTH SIDES 0F FABRIC 7'0 SEAL EDGES AND OVERCOME TENS/0N LOADS M/VE/VTOH'S manna n. FISHER FIG 2 HARRY 7. K/FOR poms/.0 a. rscnuar BYI A 77' OR/VE Y United States Patent METHOD FOR FORMING THREAD CONNECTED DUAL WALL INFLATABLE FABRIC INTO COM. POUND CURVATURES Richard R. Fisher, Akron, and Harry T. Kifor and Donald B. Tschudy, Canton, Ohio, assignors to Goodyear Aerospace Corporation, Akron, Ohio, a corporation of Delaware Filed July 15, 1966, Ser. No. 565,635 Int. Cl. 1329c 17/04 U.S. Cl. 264-89 6 Claims ABSTRACT OF THE DISCLOSURE A method is provided for forming dual wall thread connected inflatable fabric into compound curvatures with a wrinkle free surface configuration. The process involves pressurizing the fabric to slightly above ambient pressure, heating the fabric above the deformation temperature thereof, positively forming the fabric at such heated temperature to the desired shape, cooling below the deformation temperature, and releasing the positive forming action. The process is characterized by maintaining the pressure in the fabric as formed at substantially the same pressure above ambient during all steps of the process.

This invention relates to a method for forming dual Wall thread connected inflatable fabric into compound curvatures, and the specific steps which are critical to wrinkle free forming for high quality results at minimum expense.

Heretofore it has been known tht dual wall thread connected inflatable fabric has many varied and useful purposes. This fabric made under the trade name Airmat by Goodyear Aerospace Corporation must normally be made in flat sections. However, the contour between the fabrics can be controlled by varying the length of the drop yarns or threads connecting the fabrics, but this will not be effective for controlling the contour of a fabric having a uniform thickness. Further, it is difficult and expensive to form contoured fabric with variable length drop threads. Other methods to form contours in inflatable fabric have included attempts to build up and patch various thickness fabrics together, but this also has been difiicult, and expensive.

Therefore, it is the general object of the present invention to avoid and overcome the other difficulties and expensive prior art techniques for forming compound contours in inflatable fabric by very simply utilizing the ability to permanently deform synthetic fabrics when placed above their deformation temperature in a controlled manner to achieve compound contouring in flat inflatable fabric.

A further object of the invention is to provide a very simple method for forming compound curvatures in flat inflatable fabric which is inexpensive, quick, and has great adaptability to practically any compound shape.

The aforesaid objects of the invention and other objects which will become apparent as the description proceeds are achieved by providing a method for making inflatable fabric with complex curvatures which includes the steps of clamping a flat sheet of synthetic inflatable fabric around its entire periphery to seal the fabric and maintain a fixed relation to a mold having a complex contour, pressurizing the fabric and maintaining such pressure throughout the remaining steps, heating the fabric and mold to above the permanent deformation temperature of the fabric, positively forming the fabric to the contour of the mold, cooling the fabric and mold to below the deformation temperature of the fabric, and releasing the positive forming of the fabric.

For a better understanding of the invention reference should be had to the accompanying drawings wherein:

FIG. 1 is a cross sectional illustration of a female mold wherein a vacuum forming process is utilized to mold a complex contour to a sheet of flat inflatable synthetic fabric; and

FIG. 2 is a block diagram indicating the necessary and important steps comprising the process of the invention.

With reference to the drawings, the numeral 10 indicates generally a female mold having a mold surface 12 formed to a complex contour. A suitable vacuum line 14 having a control valve 16 is connected to the surface 12 so as to provide a vacuum forming process for any material placed against the surface 12, all in the usual manner known to the art.

The process of the invention is achieved by first starting with a sheet of flat inflatable synthetic fabric. This fabric is constructed as dual wall thread connected inflatable fabric such as that sold under the trade name Airmat by Goodyear Aerospace Corporation, The fabric normally is woven on a double fabric loom in flat configuration, and is open on the sides and ends between the fabric after the weaving process although the fabrics are connected by drop yarns or threads. The sides and ends of the fabric as well as the fabric itself may then be made fluid imprevious in any suitable manner such as covering with a vinyl or fluid impervious sheet so that the fabric may be inflated. The fabrics may be made fluid impervious during the weaving, The invention contemplates that suitable synthetic material for the purposes of the invention will include nylon or Dacron, although any other synthetic fabric having the properties of high strength, good flexibil ity for weaving, and being able to permanently deform at a certain temperature without losing its strength and flexibility characteristics will meet the objects of the invention.

The first step in performing the method of the invention is to clamp and seal the periphery of the sheet of flat inflatable synthetic fabric, as indicated by block 18 in FIG. 2. With reference to FIG. 1 this is achieved by a circular clamping ring 20 extending around the entire periphery of the sheet of flat fabric 17 and clamping the end portions 17A thereof in a sealed relationship so that the inflatable fabric 17 may be inflated through a suitable conduit and valve 22. Any suitable means may be utilized to hold the clamp 20 in position, such as bolts 24. The second stop then involves pressurizing the fabric 17 through the conduit 22 to a pressure only slightly above ambient pressure. For example the pressure within the fabric 17 could be in a range from about 15 p.s.i. absolute to about 17 p.s.i. absolute, where 14.7 p.s.i. absolute is atmospheric pressure. The conduit 22 contains a valve 26 which may be set to insure that the pressure within the fabric 17 remains at the desired pressure above ambient, either by adding more pressure as necessary, or releasing pressure as necessary. This step in the process is indicated by block 28 in FIG. 2.

The next step in the process is to heat the mold and fabric to the deformation temperature of the synthetic fabric or slightly thereabove, and is indicated by block 30 in FIG. 2. It should be pointed out that the deformation temperature for nylon and Dacron is approximately 300 F. There need not be any long holding of the temperature at this point, but it must be uniformly applied throughout the fabric 17 so proper deformation of all parts takes place. To this end, the invention contemplates that a suitable heated temperature range of between 275 F. and about 325 F. will properly meet the purposes of the invention. The temperature rise from ambient temperature to the deformation temperature can be as fast or slow as desired, with no adverse effects in any case.

The next step in the process involves positively forming of the heated fabric to a desired shape, as indicated by block 32. The forming is accomplished much more easily when the fabric is heated. This particular step is carried out in FIG. 1 by drawing a vacuum through line 14 so as to pull the fabric 17 into conforming relationship with the inner surface 12 of the mold 10, as is clearly shown in FIG. 1. Of course, the invention contemplates that any suitable means to positively form the fabric to the desired shape will meet the objects of the invention. Thus, this would include positive pressure forming over a male mold, vacuum forming in a female mold, gravity forming over a male mold, or any other technique to positively form the pressurized fabric to the desired contour. Naturally, when one surface of the fabric is forced to the desired contour, it automatically moves the other surface to the desired contour because of the pressurized relationship and the non-extensible length of the drop yarns connected between and holding the fabrics in the desired spaced relationship.

Deformation occurs quickly when fabric temperature is at or above the deformation temperature, and one may immediately begin to cool the fabric. This comprises the next step of the invention, as illustrated by block 34. It is necessary only to cool the fabric below the deformation temperature, and again this may be done as fast or slowly as possible, without any adverse effects. Once the fabric 17 has been cooled below the deformation temperature, it may be removed from the mold by simply releasing the vacuum and the clamp ring 20. This step is indicated by block 36 in FIG. 2. Naturally, when the fabric 17 is released around its peripheral edges, the pressure therein will escape, and suitable steps must be taken to then properly seal the peripheral edges to place the fabric in final and useful form. This may, for example, be accomplished with addition of a fluid impervious flexible skin covering each side and the peripheral edges as indicated by block 38 in FIG. 2. This skin also serves to overcome tension loads in the fabric caused during the forming described above. However, because of the forming technique described above, the fabric 17 when inflated subsequently will take the same shape as illustrated in the mold of FIG. 1 because of the permanent deformation to the synthetic fabric making up the material.

It has been found that the most important step in the entire process, and the one that makes this type of forming substantially wrinkle free and effective, is to maintain the pressure within the fabric during the forming process as uniform as possible, and only slightly above ambient pressure. This means then that after pressurization, as the mold and fabric are being heated to the deformation temperature, the pressure within the fabric will slowly increase and this must be vented off by valve 26, and that as the fabric and mold are cooled after the permanent deformation, some pressure must slowly be added to the fabric as cooling will tend to reduce the pressure. The

maintaining of the pressure as nearly uniform as possible and only slightly above ambient pressure may be suitably accomplished by any suitable pressure regulating valve currently available on the market.

The forming process of the invention may be utilized to make complex paraboloid shapes for radar reflectors, an

inflatable contoured roof for a convertible automobile, a complex contoured inflatable nozzle for a rocket engine, and articles for many other uses where this extremely simple, yet highly effective process for forming inflatable fabric to desired contours represents a distinct improvement and money saving advancement in the art.

What is claimed is:

1. A method for making dual wall thread connected inflatable fabric with complex curvatures which includes the steps of clamping a flat sheet of synthetic dual wall thread connected inflatable fabric around its entire periphery to maintain a sealed and fixed relationship to a mold having a complex contour,

pressurizing the flat sheet of fabric to slightly above ambient pressure and maintaining at least such pressure in the fabric throughout the remaining steps of the process,

heating the fabric and mold to the permanent deformation temperature of the fabric,

positively forming the pressurized fabric to the contour of the mold,

cooling the fabric and mold to below the deformation temperature of the fabric, and

releasing the positive forming of the fabric.

2. A method according to claim 1 where pressurization of the fabric is only slightly above the ambient pressure surrounding the fabric, and is maintained constant in relation to the ambient pressure throughout the remaining steps of the process.

3. A method according to claim 1 where vacuum forming is used to positively form the pressurized fabric to the contour of the mold.

4. A method according to claim 1 where gravity pressure forming is used to positively form the pressurized fabric to the contour of the mold.

S. A method according to claim 1 which includes securing a flexible skin to the surface of the fabric after forming thereof and simultaneously sealing the peripheral edges to also assist in overcoming tension loads in the molded fabric.

6. A method for making dual wall thread connected inflatable fabric with complex curvatures which includes the steps of sealing the edges of the fabric to make it fluid tight,

inflating the fabric to a pressure slightly above ambient pressure and maintaining this pressure substantially constant throughout the remaining steps,

heating the fabric to at least the permanent deformation temperature of the fabric,

positively forming the pressurized fabric to the contour of a desired mold surface, and

cooling the fabric to below the deformation tempera ture of the fabric.

References Cited UNITED STATES PATENTS 2,926,385 3/1960 Willson 26489 X ROBERT F. WHITE, Primary Examiner.

J. H. SILBAUGH, Assistant Examiner.

US. 01. X.R. 2 442, 93, 322 

